docs: added info. regarding nvme_core.multipath

docs/main/user-guides/replicated-storage-user-guide/replicated-pv-mayastor/advanced-operations/HA.md

@@ -19,6 +19,12 @@ The HA node agent looks for I/O path failures from applications to their corresp
 The volume's replica count must be higher than one for a new target to be established as part of switch-over.
 :::
 
+To ensure optimal HA in Replicated PV Mayastor clusters:
+
+- Applications constrained to nodes with the `io-engine label` (`openebs.io/engine=mayastor`) will have the Nexus preferably placed on the same node where the application is scheduled. If the `io-engine` pod on a node is in a bad state, the Nexus may be placed on a different node.
+
+- The kernel parameter `nvme_core.multipath=Y` is mandatory to enable HA functionality. Without this configuration, failover to a new Nexus cannot be achieved effectively.
+
 ### How do I disable this feature? 
 
 :::info

docs/main/user-guides/replicated-storage-user-guide/replicated-pv-mayastor/rs-installation.md

@@ -31,6 +31,12 @@ All worker nodes must satisfy the following requirements:
   * **HugePage support**
     * A minimum of **2GiB of** **2MiB-sized** pages
 
+* Enabling `nvme_core.multipath` is required for High Availability (HA) functionality in Replicated PV Mayastor. Ensure the kernel parameter `nvme_core.multipath=Y` is set during the installation. (This prerequisite is optional.)
+
+:::note
+If the application is constrained to nodes with the `io-engine label` (`openebs.io/engine=mayastor`), the Nexus is preferably placed on the same node where the application is scheduled.
+:::
+
 ### Network Requirements
 
 * Ensure that the following ports are **not** in use on the node: